<template>
		<ul class="list">
			<li 
			  class="item" 
			  v-for="item of letters" 
			  :key="item"
			  :ref="item"
			  @touchstart.prevent="handleTouchStart"
			  @touchmove="handleTouchMove"
			  @touchend="handleTouchEnd"
			  @click="handleLetterClick"
			>
			  {{item}}
			</li>
		</ul>
</template>

<script>
export default {
	name: 'CityAlphabet',
	props: {
		cities: Object
	},
	computed: {
		letters () {
			const letters = []
			for (let i in this.cities) {
				letters.push(i)
			}
			return letters
		}
	},
	data () {
		return {
			touchStatus: false,
			StartY: 0,
			timer: null
		}
	},
	updated () {
		this.StartY = this.$refs['A'][0].offsetTop
	},
	methods: {
		handleLetterClick (e) {
			this.$emit('change',e.target.innerText)
		},
		handleTouchStart () {
			this.touchStatus = true
		},
		handleTouchMove (e) {
			if(this.touchStatus) {
				if(this.timer) {
					clearTimeout(this.timer)
				}
				this.timer = setTimeout(() => {
					const TouchY = e.touches[0].clientY - 79
					const index = Math.floor((TouchY -this.StartY) / 20)
					if( index >= 0 && index < this.letters.length) {
						this.$emit('change',this.letters[index])					
					}
				}, 16)				
			}
		},
		handleTouchEnd () {
			this.touchStatus = false
		}		
	}
}
</script>

<style lang="stylus" scoped>
	@import '~styles/varibles.styl'
	.list
	  display: flex
	  flex-direction: column
	  justify-content: center
	  position: absolute
	  right: 0
	  top: 1.58rem
	  bottom: 0
	  width: .4rem
	  .item
	    line-height: .4rem
	    text-align: center
	    color: $bgColor
</style>
